1. Field of the Invention
The present invention relates to an air intake arrangement for an internal combustion engine, and in particular, relates to an air intake arrangement for an internal combustion engine for performing a so called fuel lean air/fuel ratio .[.opeartion.]. .Iadd.operation .Iaddend.wherein the engine is operated at a fuel lean side rather than the stoichiometric air/fuel ratio for improving fuel economy.
2. Description of Related Art
JP-A-62-48927(1987), for example, discloses a conventional air intake arrangement for performing a fuel lean air/fuel ratio operation wherein in an engine with two air intake valves there are provided two separate passages leading to the respective air intake valves.[., an.]. .Iadd.. An .Iaddend.intake air control valve is provided in one of the passages, .[.in.]. .Iadd.so .Iaddend.that, in a straight port, during a low engine load the intake air control valve is closed so as to increase flow velocity of the intake air flowing into the combustion chamber.[., further in.]. .Iadd.. In .Iaddend.the other passage.[., in that,.]. .Iadd.a .Iaddend.swirl port or .[.herical.]. .Iadd.helical .Iaddend.port, which is used during such low engine load condition, is bent so as to follow along the inner wall face of the combustion chamber.[., as.]. .Iadd.. As .Iaddend.a result.Iadd., .Iaddend.a swirl is caused in the combustion chamber thereby combusting speed of the mixture gas is increased and a stable combustion is obtained even with a fuel lean mixture gas.
During an idling operation of an engine, it is usually necessary to feed in a good response a small amount of air to the engine for realizing a smooth engine operation. Further, such measure is known that when auxiliary devices such as an air conditioner are rendered operative an amount of air is increased to compensate a torque consumed in the auxiliary devices in order to prevent a variation of the engine operating condition. However, in order to achieve a smooth engine operation it is desirable to be able to supply air for a torque-up use immediately when the auxiliary devices are turned on and a necessity of a torque-up occurs. Namely, it is desirable that air for torque-up use shows a good response.
Further, when a so called EGR operation is intended to be performed which improves fuel economy and cleans up the exhaust gas by reducing combustion temperature through the exhaust gas recirculation during a partial engine load, it is well known to introduce EGR gas into a collector which is a collecting portion of air intake conduits. Further, an EGR with about 0.about.20% EGR gas is recommended as a proper range for fuel economy improvement, therefore it is preferable to perform an EGR with a possible large % of EGR gas within the above range.
In the conventional air intake arrangement which is designed to generate a swirl, there is provided an intake air control valve in a main air passage near an air inlet valve, therefore there arises a problem that the intake air control valve constitutes a resistance to the intake air during an engine full load operation and effects to reduce the engine output.
Further, when the air intake valve is closed, fuel deposits onto the air intake valve and causes a problem which reduces an acceleration response of fuel supply.
Still further, a fuel injection valve, the mounting portion, fuel piping and air piping for fuel atomization for the fuel injection valve, and the air intake conduits conventionally were separately designed and assembled, the fuel injection valve is placed far remote from the center axis of the air intake conduit, as a result, an angle formed by the atomizing axis of the fuel injection valve and the center axis of the air intake conduit is increased which allows easy deposition of the fuel on the inner wall of the air intake conduits even when the air intake valve is opened, and causes a problem of reducing an acceleration response of fuel supply.
Further, since the direction of intake air is determined by the main air passage itself, it is difficult to effectively induce a swirling.
Still further, in case of the two air intake valve type engine, either a minimum flow passage cross sectional area of the swirl port has to be selected at about 1/2 of the main passage or the swirl port has to be more restricted than the straight port. In both cases, an adjustable range of the swirling strength depending on operating conditions of the engine is limited, and there arised a problem that an obtained swirl is sometimes weaker and sometimes stronger than that .[.reqired.]. .Iadd.required .Iaddend.depending on the engine rpm. On the other hand, when the intake air control valve is opened, the air intake passage is narrowed by the existence of the swirl port and the air intake characteristic of the passage including the straight port and the swirl port is deteriorated, namely which caused a problem of reducing the maximum engine output.
Further, when air for an engine idling and for a torque-up operation is introduced into the collector which is a collecting portion of the air intake conduits, there arised a problem of deteriorating a response characteristic of intake air due to the large volume of the collector.
Likely, when EGR gas is introduced into the collector, the EGR gas interfers .Iadd.with .Iaddend.the combustion, in particular, when it is required to accelerate combustion by means of swirling it is difficult to uniformly introduce the EGR gas to the respective cylinders of the engine. Further, during a transient engine operation a response of EGR gas supply delays and the combustion of the mixture gas is extremely interfered .Iadd.with .Iaddend.depending on the engine operating condition which .[.arised.]. .Iadd.created .Iaddend.a problem of impeding a large amount of EGR gas introduction.